Population inversion and gain in molecular gases excited by vibrationally excited hydrogen

ABSTRACT

Population inversion and optical gain is obtained from a gaseous mixture which includes vibrationally excited hydrogen, helium, and a polyatomic molecular gas which has a resonant energy level near the first vibrational energy level of hydrogen, and which has allowed transitions to an intermediate vibrational level lying between the resonant level and the ground state. Coherent infrared emission is observed when the gaseous system is excited in a laser system.

U it Me S iaies aten i [72] Inventors Franck T. Byme;

Carl F. Shelton, both 01' Silver Spring, Md.

[21] Appl. No. 33,411

[22] Filed Apr. 30, 1970 [45] Patented Sept. 14, 1971 [73] AssigneeInternational Business Machine Corporation Armonk, NY.

[54] POPULATION INVERSION AND GAIN IN MOLECULAR CASE EXCITED BYVIBRATIONALLY EXCITED HYDROGEN 12 Claims, 6 Drawing Figs.

52 US. Cl 331/945 [51] Int. Cl..... llflls 3/09 [50] Field of 331/94556] References Cited UNITED STATES PATENTS 3,393,372 7/1968 Vickery eta1. 331/945 Assistant ExaminerEdward S. Bauer Attorneys1-lanifin and.lancin and Maurice 1-1, Klitzman ABSTRACT: Population inversion andoptical gain is obtained from a gaseous mixture which includesvibrationally excited hydrogen, helium, and a polyatomic molecular gaswhich has a resonant energy level near the first vibrational energylevel of hydrogen, and which has allowed transitions to an intermediatevibrational level lying between the resonant level and the ground state.

Coherent infrared emission is observed when the gaseous system isexcited in a laser system.

H2 SOURCE 41 HE SOURCE POLYATOMIC GAS SOURCE HIGH VOLTAGE PULSE SOURCE23 v VACUUM PUMP PAIENTEUSEPMIHYI sum 1 or 4 F I G. 2

F I G. I

2. SOURCE HE SOURCE POLYATOMIC GAS SOURCE 2 zsvwAcuum HIGH VOLTAGE PULSESOURCE OSCILLATOR. 37

HIGH VOLTAGE D.C. POWER SUPPLY PULSE GENERATOR Ell 35 T0 ANODE 4? (f I20 T0 CATHODE 16 O CIIRRENT PULSE (200mu/DIV) N LASER FIG. 4 PULSE(ARBITRARY UNITS)- INVENTORS I 1 l FRANCIS T. BYRN TI I PS/DIV) CARL rsumon BYQf/W/V- ATTORNEY PATENTED SEP! 4197:

SHEET 2 OF 4 aoow econ

20 romuzu coon n w m SHEEI 3 BF 4 PATENTEDsEm nn II; we?

:6 I wzizhz 6 555 Nan;

ooow

coon

POPULATION INVERSION AND GAIN IN MOLECULAR GASES EXCITED BYVIBRATIONALLY EXCITED HYDROGEN BACKGROUND OF THE INVENTION Thisinvention relates to infrared lasers in which a polyatomic molecular gasis employed as the active constituent in the laser medium. Inparticular, this invention concerns the use of the metastable state of adiatomic molecule to induce population inversion and optical gain inpolyatomic molecular gases.

The energy level spectra of molecular gases are much more complex thanthose of atomic gases. A polyatomic molecule, even when in theelectronic ground state, has mechanisms which store energy and which maybe excited. There are two such mechanisms known: vibration according toa periodic motion and rotation about the molecules center of mass. Thesevibrational and rotation energies exist in certain welldefined states,analogous to the discrete states of the electron orbits of atoms. In thesimplest structure, a diatomic molecule, several approximately equallyspaced vibrational levels exist; for each of these levels, there are anumber of rotational levels. This accounts for the very complicatedenergy level diagrams of molecular gases. As in the electronic levels ofatoms, the higher vibrational energy levels of molecules are ordinarilyless populated than the lower vibrational energy levels. To achievelaser emission, the population of these levels must be reversed, i.e.,population inversion must first be caused to occur.

C. K. N. Patel was apparently the first person to demonstratevibrational level inversion in carbon dioxide in his article in PhysicalReview Letters, Nov. 23, 1964, p. 617. Soon thereafter, Patel showedthat nitrogen in its metastable vibrational level (v==l) could be usedto selectively populate an upper level of carbon dioxide throughresonant transfer via inelastic collisions. The 001 level of carbondioxide is nearly resonant with the v=l level of nitrogen. Laseremission near l0.6 microns was observed. Since that discovery, carbondioxide lasers have been developed which emit coherent radiation withenormous power. Perhaps the most notable achievement has been a C laserwhich is one meter long and has a continuous output of one kilowatt.Continuous output power of 8.8 kw. has been obtained from CO lasers ofmuch greater length and still greater power is theoretically achievable.Patel and others have also demonstrated that CS and N 0 will yield laseremission around 10 microns when excited by vibrationally excited N Apolyatomic molecular gas laser which will efficiently emit radiation inthe region below 10 microns has been sought after. An N -CO laser whichgenerates radiation at a wavelength about microns has been demonstrated.However, it operates most efiiciently at the temperature of liquidnitrogen; at room temperature this laser is inefficient and thus has notfound wide application.

The use of a diatomic gas which has a higher quantum of energy in itsmetastable first vibrational level than nitrogen has been suggested byothers in' this art. It appeared that the diatomic molecule hydrogenwith an energy level of 4159.2 cm." (2.41 microns) in its metastablefirst vibrational level could be used to excite a polyatomic moleculewhich has an upper vibrational level which is nearly resonant with thatof hydrogen (around 4160 cm"). Similar to N the v=l level of H at 4159.2cm has no permanent dipole moment with respect to the v=0 level. Thus,the v=l level of H is metastable and cannot relax via radiativetransitions. The sole depopulation mechanism from the v=l to the v=0level is through inelastic collisions with other molecules or the wallsof the enclosing container or envelope. In addition, the cross sectionfor excitation of the vibrational mode of H by electron impact in a lowpressure gas had been measured.

Because of this prior word by others in the field, the followingreactions were expected:

where H *(v=l represents the first vibrational energy level of H in theelectronic ground state. 2*("= 2( )-|-M*= where H (v=ll rsas explairTedaBHVeWTEpresents the where v,,,,,,,. is the frequency radiated when theM* molecule drops to a lower energy level.

However, attempts to achieve population inversion and optical gain withI'l -polyatomic molecule systems have been unsuccessful. ln one reportedseries of experiments, gases of H 0, NH HCN, and CH, were tested. Eachof these molecules has an upper vibrational level which is nearlyresonant with the first vibrational level of H in its ground electronicstate [H "(v=l )1 and has allowed transitions to a level intermediatebetween the upper level and the ground state. The oscillator apparatusused was similar to that used by Patel in achieving emission in hisN,-CO No laser emission was observed for any mixture. In an independentseries of experiments, the present inventors attempted to excite NHC,H,, CH C H and C H with H No laser emission was observed. The apparentreason for this failure is the inability to excite the hydrogen from itsground state H,(F0) to its first vibrational level H*(v=l SUMMARY OF THEINVENTION It is therefore an object of this invention to obtainpopulation inversion and gain from a molecular gas by exciting the gaswith a vibrationally excited diatomic molecule which has metastablevibrational levels higher than those of nitrogen.

It is a further object of this invention to provide an infraredmolecular gas laser which emits radiation at wave lengths in the regionbelow 10 microns.

These and other objects are achieved by vibrationally exciting hydrogento overpopulate a near-resonant upper vibrational level of a polyatomicmolecule. The molecule is a polyatomic gas having an upper energy levelwhich is nearly resonant with the first vibrational level of hydrogenand which has allowed transitions to an intermediate level lying betweenthe resonant level and the ground state. Helium must be added to themixture. The addition of helium allows one to adjust the electrontemperature and the electron density of the gaseous mixture. This shiftsthe energy distribution of the electrons to more favorable values forexciting by electron impact the vibrational levels of hydrogen.Successful emission occurs only after helium is added to thehydrogen-polyatomic molecule mixture and the pressure of the gases isadjusted so that the energy distribution of the electrons are mostfavorable to exciting the H to its H *(v=l) level.

Gases such as helium, xenon, and neon had previously been added to a N-CO laser to increase the power output. The effect of these gases is toredistribute the rotational distribution of the upper and lowertransition levels of the C0 This prevents the depletion of the upperrotational level of the CO and speeds up the depletion of the lowerrotational level. See, e.g., Effects of C0,, He, and N, on theLifetimes... of CO Laser Levels..., P. K. Cheo, J. Appl. Phys., Vol. 38,09, 1967, pp. 3563-3567. It has also been hypothesized that collisionsbetween He atoms and CO molecules tend to thermalize the rotationallevels of the excited CO molecules. See High Power Laser Action in CO-He Mixtures," Moeller et al., Appl. Phys. Lett., Vol. 7, 010, 1965, pp.274-476. Unlike the present invention, these gases have no discernibleeffect on the N, in a Ng'cog laser. This is demonstrated by the factthat xenon, which increases the output of a N CO, laser, has a lowerionization potential than N Hence, it is not capable of increasing theelectron temperature in the N CO gas as He does in the H mixture of thepresent invention.

The invention will be more fully understood by referring to thefollowing detailed description taken in connection with the accompanyingdrawings, forming a part thereof, in which:

FIG. I is a simplified schematic representation of a coherent lightgenerator containing the gaseous mixtures of the present invention.

FIG. 2 is the circuit used for providing pulsed excitation of thegaseous mixtures in block diagram form.

FIG. 3 is a simplified energy level diagram of acetylene 2 1)- FIG. 4 isa tracing from an oscilloscope pattern showing the output of the lasersystem compared to the input current from the excitation source.

FIGS. 5 and 6 are simplified energy level diagrams of methane (CI-I andammonia (NI-I respectively.

Referring now to FIG. 1 of the drawing, there is shown an envelope 10filled with the gaseous mixture of this invention. Envelope 10 may be atube fabricated of glass with a length of several inches to severalfeet, depending on the output power desired. The diameter of theenvelope may vary from fractions of an inch to several inches. In oneembodiment of the invention, the inner diameter of envelope 10 wasone-half inch and the length was 1.4 meters. Jacket 11 surroundsenvelope 10 for cooling purposes. It may contain any number of coolants,such as water or liquefied gases, depending upon the desired temperatureof the gaseous mixture. The envelope is supported between supports 12,and 13. Reflectors 14 and 15 are used to define an optically resonantcavity. The reflectors may be plane-parallel, semiconfocal, confocal, orconcentric. To achieve exact alignment, which is critical, stainlesssteel bellows 8 and 9 are used to allow alignment of the reflectors. Inthe present embodiment, both reflectors are highly reflective, broadbandmirrors. Reflector 14 is a gold-coated mirror with a radius of curvatureof 5 meters; reflector 15 is a flat, goldcoated BaF crystal with a holeof H2 mm. diameter in the gold coating. The hole allows a small fractionof the energy inside the resonant optical cavity formed by reflectors 14and 15 to be coupled out of the cavity. It will be understood by thoseof skill in this field that the reflectors may also be of the narrowband type, selected to reflect only a chosen wavelength.

Means for producing electrical current pulses within envelope 10,thereby exciting the mixture, comprise cathode 16, anode l7 and highvoltage pulse source 20. The apparatus and operation of pulse sourcewill be discussed at greater length in a succeeding secton of thisapplication in conjunction with FIG. 2. Free electrons are the initialexcitation mechanism in the system and are supplied by cathode 16 and byionization of the gases within envelope 10. Both the cathode and anodemay be composed of stainless steel, nickel, tungsten, or other suitablematerial. In the preferred embodiment, the cathode and anode are nickel.

A continuous flow of gases comprising the lasing medium is providedthrough plasma envelope 10 by means of a gas inlet 21 and gas outlet 22which is connected to vacuum pump 23. Sources of hydrogen, helium, andthe polyatomic gas 40, 41, and 42, respectively, are connected to gasinlet 21 through suitable flow meters 50, needles valves 51, and tubing52. Each flow meter and associated needle valve control the partialpressure and flow rate of its associated gas. A capacitor manometerpressure head 54 connected to tubing 52 measures the total partialpressure of the gases before they enter discharge envelope 10. Meter 53converts the pressure head measurement into an electrical readout. Laseremission through the aperture in reflector 15 may be sensed by any of anumber of commercially available detectors (not shown), such as a Ge-Audetector.

The high voltage pulse source 20 shown in FIG. 1 may comprise severaldifferent forms. The preferred embodiment, shown in FIG. 2, comprises ahigh voltage DC power supply 31 connected to a resistor-capacitorcombination 32, 33. The terminal point 28 between resistor 32 andcapacitor 33 is connected to anode 17 and one side of resistor 34. Theterminal point 29 of resistor 34 opposite anode 17 is connected tocathode l6 and the plate of thyratron 35. Oscillator 36 and pulsegenerator 37 are employed through transformer 38 to repetitively operatethyratron 35. In the operation of one embodiment of this invention,supply 31 provided is a voltage of l0 kilovolts through resistor 32 tocharge capacitor 33. The value of power supply 31 is chosen to exceedthe breakdown potential of the gas in envelope 10. This potential isdependent on the particular gas mixture used and the pressure of the gaswithin envelope 10. Resistor 32 and capacitor 33 have values of kilohmsand 0.02 microfarads. respectively. Resistor 34 has a value of l megohm.Oscillator 36 is operated at varying rates between 1 and 250 Hz. torepetitively switch thyratron 35 at the same rate. With the thyratronturned on, plate 35 and cathode 16 are effectively at or near groundpotential. This causes the charge stored in capacitor 33 to be releasedacross the envelope 10 in FIG. 1 between anode l7 and cathode 16. Itwill be recognized by those of skill in the art that the design andconstruction of the high voltage pulse source are not inventiveMoreover, AC DC or R.F. excitation rather than pulsed excitation havebeen used successfully for other molecular gas lasers. However, thehigher excitation power available from a short pulse makes pulsedexcitation more favorable.

It will be recognized that the total energy of the pulse must be lowenough not to dissociate the gas and high enough to vibrationally excitethe gas. In the preferred embodiment of this invention the energy of thepulse was about 1 joule.

In the preferred embodiment of this invention population inversion andoptical gain has been achieved using a flowing mixture of H -C I-I-I-Ie. Laser emission has been observed using the apparatus described inFIGS. 1 and 2. As will be further discussed, acetylene (C I-I has thegreatest number of possible laser transitions of those molecules whichare known to have vibrational energy levels nearly resonant with the l-l*(v=) energy level.

Acetylene is a linear symmetric molecule with the configuration l-IC CH.For this system, there are five normal modes of vibration, designated bythe standard notation v ..,v The notation 2g, 21;; rrg, and Try.suffixed to the vibrational modes represent the species or symmetrytypes of the normal vibrations. The last two vibrational modes aredegenerate bending modes, denoted by superscripts. Those interested in amore complete explanation of this notation should consult Herzberg,Infrared and Raman Spectra, D. Van- Nostrand & Co., 1945. The pertinentvibrational levels of C I-I, are shown in FIG. 3 to which reference isnow made.

FIG. 3 is a much simplified vibrational energy level diagram of C 11 Itwill be seen that the 10001 level at 4091 cm. is at near resonance withthe H *(v=l) level at 4159.2 cm., and the possibility of resonantvibrational energy transfer via an inelastic collision exists as shownby the formula:

' +C I-I *(10001 )+AE 68:2 cm- Where 0000 0 represerfis the groundvibrational level and 10001 is at 4091 cm.. An acetylene molecule in the10001 'n'p. level could then decay radiatively to 10000 2g level at3373.7 cm., satisfying the wg selection rule. Because the 10000 25 levelis then in close Fenni resonance with both the 01011 211i and 00100 El:levels at around 3290 cm., a rapid exchange of energy might occur eventhough the u g selection rule is violated. The molecule may decay fromany of these three levels, 10000 2, 0101 1 211 and 00100 sit, by allowedwg transitions. The decay transitions to lower energy levels areindicated by the dotted lines and the radiation which would be emittedis given in units of microns alongside the dotted lines in FIG. 3. Forexample, a decay from the 10000 E level to the 01001 rrp. level wouldresult in the emission of radiation of 14.9 microns.

The 0002l 11p and 01000 2 levels are also in close Fermi resonance andmay rapidly exchange their energies. Some of the allowed vibrationaltransitions for the acetylene molecule are given in table I. It shouldbe noted that the energies given in table I are only the vibrationalenergy level differences for the transitions specified and do notinclude rotational levels. Because the molecules in each vibrationalstate are distributed according to Boltzmanns distribution, the actualenergy level differences can be calculated precisely.

TABLE I.TRANSITIONS OF C H,

Vibrational transition Energy Wavelength I000] lip-H0000 31* 717.03111.- 13. 954.1 imam-00001 [In 2.6426 cm.' 3. 78 ltXlOO Sg -$1001 I'lu672.2 cmf 14. 90a (IJO TIP- 000? Hp 7. 059 00000 lip-)OOOUO UL. 6. 22;;0002 1 I'lp-tOIXllO II" 7. 45;: 0l01 l Kip-)Oltlll 3g 7. 57;: CD100Zn)01000 22* 7. 61;: 01000 Zg*- 00.r01 Hp. 8. 03;: 10000 Zg*)00t03 Hp 8.64;: 10001 Ila- 01000 Eg 4. 724

As can be seen from the large number of allowed transitions in C 14,shown in FIG. 3 and table 1, selective population of the 10001,vibrational level from resonant vibrational energy transfer fromH,'(v=l) offers many possibilities for new laser emission lines in thenear infrared region of the spectrum.

Using the apparatus shown in FIG. 1, a H -QH -He mixture which wasextremely rich in He was used as the lasing medium. Pulsed excitation,rather than DC excitation, from pulse source was used because theelectron density resulting from the former is at least an order ofmagnitude higher than the latter for the gas mixture used. Laseremission was observed at 8.04 microns on a single line with norotational lines. A Jarrell-Ash model 1 meter Czerny-Tumer spectrometerwith a 98 groove/mm. IR grating blazed at 7 microns was used to measurethe wavelength of the laser emission.

At a temperature of 300 K., emission was obtained from a flowing mixtureof 2.0 torr H 1.0 torr C H and between 10.0 to 20.0 torr He. The Bepressure was varied between 10 and 20 torr without affecting the laseremission. Attempts at achieving emission from a C H plasma, a C H- l-leplasma or a C l-l H plasma failed.

At a bath temperature of approximately 200 l(., emission was obtainedfrom a flowing mixture over a wider range of partial pressures: l to 2torr H 2 to 4 torr C H and 10 to 20 torr He. In this demonstration thecoolant in jacket 11 of FIG. 1 was maintained at 200 K. The temperatureof the gas mixture within envelope 10 was not measured. The improvementin pressure ranges with lower temperatures is not unexpected. Coolingincreases the rate at which the ground state of the molecules isdepopulated.

FIG. 4 of the drawing illustrates a single example of the results ofthis invention. FIG. 4 shows a combined graphical representation of acurrent pulse discharged through envelope l0 and a laser output pulseobserved from a flowing mixture of 2.0 torr H 1.0 torr C H,, and 20 torrHe at T=300 K. The current pulse is seen to average around 200 mA foraround 200 microseconds. The total energy input is around 1 joule. Thelaser output pulse has a pulse width of around microseconds and a peakpower of 5.7 watts at 8.040' *0.00l2 microns. in this demonstration,laser emission was observed at current pulse repetition rates of from 1p.p.s. to 250 p.p.s. from power source 20. There is avibrational-rotational transition, the Q(l2) line, on the 01000 2-00001rrp. band of C2": which has a calculated wavelength of 8.0404 microns.The theoretical normalized gain of this vibrational-rotational bandpeaks near Q( 12) for small values of vibrational level inversion. Thusthe laser emission appears to originate from the 002 line of the 010002-00001 7T!!- band of can. Assuming that this is so, the laser is thenfunctioning as a classical four-level laser. As shown in FIG. 3, pumpingtakes place through a resonant vibrational energy transfer from the v=llevel of H which has been excited by electron impact in the helium richplasma:

The excited hydrogen then vibrationally excites the acetylene from itsground state to its 10001 level by inelastic collisions: v (6) H *(0= 1)+C H (00000) H (1.-=0)

The C l-i 19001) level can then make allowed transitions to the 01000 23level which is the upper laser level.

The radiative transition occurs from the 01000 level to the 0000i rrp.level:

(7) C H (0l000) C,H,( 00001 )+hv,,,,., =8.040 microns The lower laserlevel, the 00O0l1ry. level, then is depopulated through the stronglyallowed 0000l1rp.-00000 2g transition.

This discovery may lead to laser emission at other wavelengths in C H orother gases which have resonant vibrational energy levels with the v=llevel of H With narrowband reflectivity mirrors, for example, laseremission near 4 microns might be produced on the 10000 23 -00001 rrp.band of C H This would have a potential efficiency of about 65 percent(compared to 40 percent for the 10 micron C0, laser emission). The 8micron line on the 01000 29 00001 'Ilp. band, on the other hand, has apotential quantum efficiency of about 30 percent.

Referring now to FIG. 5, the vibrational energy level dia- TABLE2.TRANSITIONS OF CH4 Vibrational transition Energy Wavelength 0011-)00101,292.9 (I'm- 7. 75;; 0011-)0001.-- 3. 25a 0102-+0002- 6. 57;;0102-M1101- 7. 70 1001-)1000. 7. 72;; 1001-)0001. 3. 42;;

Ammonia is a symmetrical pyramidal molecule with four normal modes. Thevibrational energy levels of NH are shown in FIG. 6. Some of thepossible transitions resulting from vibrational energy transfer from Hare shown in FIG. 6 and listed in table 2. The 0102, 1100, and 0110levels are all situated near the 4159.2 cm. H *(v=l level with the 4176cm. 0102 level having the nearest resonance. The two energy levels shownfor each of these vibrational modes come about from the fact that the vmode is split by inversion doubling where the N atom is moved throughthe H plane to an equivalent position on the other side.

TABLE 3. TRANSITIONS OF NH:

Vibrational transition Energy Wavelength 0102-M1100 3,248 cmr 3. 070102- 0o01- 1 3. 0102-W002- 10. 00 0102-M1101. 5. 8715 TABLE4.TRANSITIONS OF (32H;

Vibrational transition Energy Wavelength va+2v1--vm va 2,865 cm.- 3. 49pva+2v1 -vw 2v1. 2,309 cm 4. 33;; v3+2v -ll-Vw)m 3,212 cmr 3. 12;;

In summary, the present invention has demonstrated that any polyatomicmolecule with the following two characteristics is a candidate for laseremission:

1. it must have an energy level which is nearly resonant with the H*(v=l level; and

2. it must have allowed transitions between the resonant level and theground state.

Helium is added to establish the pressure and composition of the gasmixture at a level which yields an electron energy distribution which isfavorable to vibrationally excite the H molecules. Acetylene has beenused as the preferred polyatomic gas because it has more possibletransitions than any other gas known to have the above twocharacteristics.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. A laser for producing coherent infrared radiation comprising:

a pair of spaced apart reflectors forming a resonant cavity forreflecting infrared radiation;

an envelope disposed between the two minors;

a gaseous mixture of hydrogen, helium, and a polyatomic molecule whichhas a resonant energy level near the vibrational energy level of thefirst metastable state of hydrogen, and which has allowed transitionsbetween the resonant energy level and the ground state; and

means for exciting the gas mixture by electrical energy to raise thehydrogen to its first metastable state, thereby to induce laser emissionby vibrationally exciting the polyatomic molecule.

2. A laser as in claim I wherein the polyatomic gas is selected from thegroup consisting of acetylene, methane, ammonia, and ethylene.

3. A laser as in claim 1 wherein the means for exciting the gaseousmixture comprises pulsed excitation means.

4. A laser as in claim 1 further comprising:

means for continuously flowing the gaseous mixture at selected partialpressures within the envelope; and

cooling means for controlling the temperature of the gaseous mixture S.A laser as in claim 4 wherein the polyatomic gas is acetylene and thepartial pressures of the hydrogen, acetylene, and helium have thefollowing ranges, respectively: 2 to 4 torr, l to 2 torr, and 10 to 20torr.

6. A laser as in claim 4 wherein the polyatomic gas is acetylene, thetemperature of the cooling means is around 300 K. and the partialpressures of the hydrogen, acetylene,

and helium are 2 torr, 1 torr, and between 10 and 20 torr,

respectively, thereby to cause laser emission at 8.040 microns. 7. Alaser as in claim 5 wherein the temperature of the cooling means isaround 220 K., thereby to cause laser emission at 8.040 microns.

8. A method for inducing population inversion in an envelope containinga gaseous mixture of hydrogen, helium, and a polyatomic molecule whichhas a resonant energy level near the first metastable state of hydrogenand which has allowed transitions between the resonant energy level andthe ground state comprising:

exciting the gaseous mixture by electrical energy to raise the hydrogento its first metastable state, thereby inducing population inversion byvibrationally exciting the polyatomic molecule.

9. A method as in claim 8 further comprising the steps of:

continuously flowing the gaseous mixture within the envelope at selectedpartial pressures for each gas; and controlling the temperature of theenvelope containing the gaseous mixture.

10. A method as in claim 9 wherein the polyatomic molecule is acetylene.

11. A method as in claim 10 wherein the selected partial pressures ofthe gases are: 2 torr, between 10 and 20 torr, and 1 torr for hydrogen,helium, and acetylene, respectively; and

the temperature of the envelope is around 300 K.

12. A method as in claim 10 wherein the selected partial pressure of thegases are: between 2 to 4 torr, between 10 to 20 torr, and between 1 to2 torr for hydrogen, helium, and

acetylene, respectively, and

the temperature of the envelope is around 220 K.

" UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,605,038 Dated September 14 1971 lnventofls) Francis T. Byrne and CarlF. Shelton It is certified that error appears in the above-identifiedpatent and that said Letters Patent: are hereby corrected as shownbelow:

w Column 4, lines 53, 55, 57, "4091 cm should read -409l cm' Column 4,line 32, "H *(v=)" should read H *(v=l).

Column 5, line 30, "300'K" should read -300K-. Column 5, line 35, "C H Hshould read C H H Column 6, line 3, "01000 level" should read 0l000 2level. Column 6, line 22, "4159.2 cm should read --4159.2 em- Column 6,line 41, 4159.2 cm and "4176 cm should read 4l59.2 cm and 4l76 cmrespectively.

Column 6, line 59 "4206.7 em should read 4206.7 cm Column 6, line 60"4159.2 cm shou (51 read --4159.2 em

In Table 4, that portion which reads "v +2v +V10 v should Signed andsealed this 1st day of August 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

2. A laser as in claim 1 wherein the polyatomic gas is selected from thegroup consisting of acetylene, methane, ammonia, and ethylene.
 3. Alaser as in claim 1 wherein the means for exciting the gaseous mixturecomprises pulsed excitation means.
 4. A laser as in claim 1 furthercomprising: means for continuously flowing the gaseous mixture atselected partial pressures within the envelope; and cooling means forcontrolling the temperature of the gaseous mixture.
 5. A laser as inclaim 4 wherein the polyatomic gas is acetylene and the partialpressures of the hydrogen, acetylene, and helium have the followingranges, respectively: 2 to 4 torr, 1 to 2 torr, and 10 to 20 torr.
 6. Alaser as in claim 4 wherein the polyatomic gas is acetylene, thetemperature of the cooling means is around 300* K. and the partialpressures of the hydrogen, acetylene, and helium are 2 torr, 1 torr, andbetween 10 and 20 torr, respectively, thereby to cause laser emission at8.040 microns.
 7. A laser as in claim 5 wherein the temperature of thecooling means is around 220* K., thereby to cause laser emission at8.040 microns.
 8. A method for inducing population inversion in anenvelope containing a gaseous mixture of hydrogen, helium, and apolyatomic molecule which has a resonant energy level near the firstmetastable state of hydrogen and which has allowed transitions betweenthe resonant energy level and the ground state comprising: exciting thegaseous mixture by electrical energy to raise the hydrogen to its firstmetastable state, thereby inducing population inversion by vibrationallyexciting the polyatomic molecule.
 9. A method as in claim 8 furthercomprising the steps of: continuously flowing the gaseous mixture withinthe envelope at selected partial pressures for each gas; and controllingthe temperature of the envelope containing the gaseous mixture.
 10. Amethod as in claim 9 wherein the polyatomic molecule is acetylene.
 11. Amethod as in claim 10 wherein the selected partial pressures of thegases are: 2 torr, between 10 and 20 torr, and 1 torr for hydrogen,helium, and acetylene, respectively; and the temperature of the envelopeis around 300* K.
 12. A method as in claim 10 wherein the selectedpartial pressure of the gases are: between 2 to 4 torr, between 10 to 20torr, and between 1 to 2 torr for hydrogen, helium, and acetylene,respectively, and the temperature of the envelope is around 220* K.